1. Field of the Invention
The present invention relates to a method for operating a base station of a mobile wireless system, in particular of a mobile communications network, wherein said base station is configured to operate in different operation states, wherein said operation states at least include an active operational mode, in which the radio interface subsystem of said base station is fully activated, and a low-duty operational mode with reduced radio transmission activity.
Furthermore, the present invention relates to a base station for deployment in a mobile wireless system, said base station being configured to operate in different operation states, wherein said operation states at least include an active operational mode, in which the radio interface subsystem of said base station is fully activated, and a low-duty operational mode with reduced radio transmission activity.
2. Description of the Related Art
Energy consumption, electromagnetic emissions and interference are important factors which may influence the performance and the acceptance of products involved in wireless broadband communication. For example, in the document of the European Commission “Code of Conduct on Energy Consumption of Broadband Equipment, Version 3”, Nov. 18, 2008 it is stated that “The potential new electrical load represented by this (i.e. broadband) equipment needs to be addressed by EU energy and environmental policies. It is important that the electrical efficiency of broadband equipment is maximised”. Apart from conventional base stations, this is an especially important factor for so called femtocell base stations (also known as home base stations, home BTS, picocells, home NBs, home eNBs, femtocell access points (FAPs), or femto radio base stations), which are devices being installed by customers in their premises.
There is currently an interest from mobile network operators to deploy such femtocells, which would be installed within the homes of the operators' customers themselves in a “plug-and-play” manner (see for reference Airvana whitepaper, “Femtocells: Transforming The Indoor Experience”). Such femtocells are low power mobile base stations, currently being developed and standardized for both 3G and 4G networks, at the edge of the operator network. Femtocell base stations are connected to a normal broadband internet connection, and the radio interface is based on wide area cellular network standards such as WiMAX (Worldwide Interoperability for Microwave Access), UMTS (Universal Mobile Telecommunications System) or 3GPP LTE (Long Term Evolution).
One reason for the introduction of femtocells is the increase of operator network coverage for the sake of a better user experience and therewith to make a big step towards fixed-mobile-convergence. Like Wi-Fi access points, femtocells are designed to be deployed in home and office environments in order to give good coverage in the respective area and deployment of high density is expected in areas with high population or office density. However, the deployment of femtocells comes along with drawbacks of which one is interference effects between macro and femto levels of the network. Since femtocell base stations are often deployed in the same licensed spectrum as the wide area network of the operator it is important to configure the radio interface correctly to avoid interference with other base stations. Generally, femtocell networks in a dense deployment are interference limited, meaning that any measures to decrease inter-cell interference will benefit directly to user QoS and system capacity.
Femtocell base stations have some unique properties which distinguish them from other wireless devices like macro-cell base stations or WiFi access points:
1. Although customer-deployed, femtocell BSs are part of an operator's radio access network with similar requirements as macro-cell base stations. For example, the IEEE 802.16m SRD (IEEE 802.16m-07/002r6 Requirements for the P802.16m-Advanced Air Interface”, IEEE 802.16 Broadband Wireless Access Working Group, 18. Sep. 2008) lists hand-overs and synchronization to macro-cell BSs and femtocell BSs as requirements. This implies that a femtocell BS has interfaces to higher layer network elements of the operator, like the ASN-GW (Access Service Network Gateway) in case of WiMAX.
2. Femtocell BSs are also under the direct physical control of the customer, which means that they can always be switched on and off manually. To avoid uncontrolled shut-downs and its potentially negative effects on the overall network stability, the femtocell BS should implement mechanisms to avoid uncontrolled device shutdowns in order to maintain network stability and user quality of service.